Microstructures and mechanical properties of squeeze cast in-situ TiB2/2024Al composite fabricated by applying ultrasonic vibration during solidification

Abstract

The ultrasonic vibration is widely applied to break the agglomeration of tiny TiB2 reinforcements in molten TiB2/2024Al composite. To date, plenty of researches have focused on the effects of ultrasonic vibration in melt preparation, but few works has been done on introducing the ultrasonic vibration into the solidification process. In the present work, ultrasonic vibration was applied during squeeze casting of solidifying melt to fabricate in situ TiB2/2024Al composites. The effect of ultrasonic vibration and specific pressure (pressure on per unit area) on solidification behavior of α-Al matrix, matrix-reinforcements interface behavior and distribution of reinforcements were also discussed. The results suggested that although the mechanical strength changed little, the elongation to fracture was promoted evidently as the ultrasonic amplitude increasing (ultrasonic gravity casting). When the amplitude was 70 μm, the elongation to fracture, Vickers hardness, yield strength and tensile strength of composites were 15.9%, 85 HV, 119.5 MPa and 288 MPa (increased by 20.4%, 9.2%, 4.8% and 3.3% compared to gravity casting), respectively. As for the ultrasonic assisted squeeze casting, the average grain size was firstly refined from 58 μm to 43 μm when the specific pressure was promoted from 0 to 50 MPa (the ultrasonic amplitude was 40 μm). However, the microstructures were coarsened and the mechanical properties were deteriorated as further increasing the specific pressure. When the specific pressure was 50 MPa, the elongation to fracture, yield strength, and tensile strength were 15.8%, 116 MPa, and 288 MPa (increased by 19.7%, 1.7% and 3.2% compared to gravity casting), respectively.